Every year around November, millions of gamers from around the world get excited for one game franchise: Call of Duty. From its humble beginnings as a World War 2 series, the franchise has seen many evolutions. With each iteration in the series, it seems that sales continue to skyrocket. This list ranks the ten major Call of Duty titles in terms of units sold (excluding handheld exclusive titles, as well as Call of Duty: Finest Hour,Call of Duty 2: Big Red One, and Call of Duty: World at War- Final Fronts).

10 Call of Duty -- 4.5 million units sold

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This is the one that started it all. A product of Infinity Ward, the original Call of Duty altered the landscape of FPS war games. One of the many innovations Infinity Ward contributed to gaming through Call of Duty was the surrounding of the player by AI that actually helps the player. It was rare to see a group of AI help the player, and it would set a trend that is still seen today. Soviet and British troops also got their story told in the game due to the creative three-tiered campaign. Players took control of not just one soldier, but three (one from America, one from Russia, and one from Great Britain). Through November 2013, Call of Duty sold 4.5 million units.

9 Call of Duty 2 -- 5.9 million units sold

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Released two years after the original Call of Duty, the second entry in the series improved many aspects of its gameplay. A feature widely praised, the regenerating health bar, has come to be a staple of the series. Keeping a varied campaign (four playable protagonists), Call of Duty 2 is a bit more cinematic than its predecessor. These cut scenes were praised at the time as "breathtaking". On the multiplayer front, Infinity Ward decided to give some control to the players. They released Call of Duty Radiant in 2006, which allowed the player to create their own multiplayer and single player maps. Sales were given a helping hand as the game was released as a launch title for the Xbox 360 in countries such as Europe, Asia, and South America.

8 Call of Duty 3 -- 7.2 million units sold

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With the first two action packed shooters quickly gaining popularity, the third instalment of the Call of Duty series continued to add to the already successful formula. The campaign revolved around four different characters from various countries. As much as Call of Duty was known for its terrific campaigns in the first series of games, Call of Duty 3's multiplayer began to draw in competitive players. In addition to the 24(max)-player matches on the PS3 and Xbox 360, the third instalment in the series also added two game modes. Players had the option to choose a mode dubbed "Normalized Mode," which adjusted the kill boxes to those of the previous instalments. Call of Duty 3 garnered many awards, including an Outstanding Achievement for Sound Design Award in 2007.

7 T7. Call of Duty 4: Modern Warfare -- 15.7 million units sold

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This is where the Call of Duty series really burst into the mainstream. Infinity Ward modified the game just enough to rake in players worldwide. Modern Warfare is the first game in the Call of Duty series to be set during modern times. Besides an award-winning campaign, Modern Warfare introduced a staple to the multiplayer genre that lasts to this day: the kill streak. Players now had the option to earn up to three kill streaks, granted they amass the required number of kills to achieve them. With high ratings from many gaming publications and a host of awards to its name, Modern Warfare is widely considered to be the best game in the Call of Duty series. Its popularity definitely shines, as it has sold 15.7 million copies throughout the world.

6 T7. Call of Duty: World at War -- 15.7 million units sold

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With a Call of Duty title now being bounced back and forth between two developers, the follow-up game to 2007's Modern Warfare transported the player back to the trenches of World War 2. While the game may not have received the accolades of its predecessors, World at War did spark a gameplay mode that has been present in every Call of Duty since World at War's release. The massively popular "Zombie" mode pits a group of players against waves and waves of Nazi zombies. With a great mixture of teamwork and pulse-pounding horror, many people consider the "Zombie" mode to be the best part of the game. Treyarch's game actually sits at a tie with its predecessor, Modern Warfare, with 15.7 million units sold globally.

5 Call of Duty: Modern Warfare 2 -- 22.7 million units sold

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With a massive hit on their hands in the form of the original Modern Warfare, Infinity Ward decided to create a direct follow-up to their genre-defining 2007 game. Many aspects of the game were tweaked and re-introduced, keeping it familiar yet just different enough to satisfy most players. Among the changes to the gameplay, the creative team added 12 kill streaks (in addition to the 3 from the original), a "Spec Ops" Mode, and host migration (if a player hosting a game has a bad connection, the game will find the most opportune connection in the lobby and make them host). A wealth of awards has been showered down on Modern Warfare 2, including Best Shooter and Best Multiplayer Awards from the Spike Video Game Awards. Modern Warfare 2 remains one of the best entries in the series.

4 Call of Duty: Ghosts -- 23.8 million units sold

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One of the first Call of Duty games not to blow away gamers, Ghosts was given mixed to positive reviews by both magazine publications and players. After the tremendous success of Black Ops: II, Ghosts had a tall order to fill. Infinity Ward tried to grab players' attention, introducing an ever growing amount of kill and death streaks, as well as a new game mode called "Extinction". The amount of customization the player had over their character was also a new touch. Ghosts even introduced the choice to play as a female soldier. Though selling 23.8 million units, many feel this is the first Call of Duty that may have taken a step backwards rather than forwards.

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3 Call of Duty: Black Ops 2 -- 24.2 million units sold

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Switching focus from solely modern and historical events, Black Ops II is the first game in the Call of Duty series to make the leap into the future. With some of the events in the game taking place in the future, Treyarch took a gamble...and succeeded. This Call of Duty feels distinctly different from the others. This feeling is recognized by many reviewers, all pointing to two major changes. First, the campaign is presented in a non-linear fashion. Certain choices and actions the player takes during the game affect missions they can unlock. The game even spouts multiple endings based on these decisions. Following in the footsteps of Modern Warfare 3, kill streaks were modified to score streaks. Not only do kills reward the player with attachments and perks, but performing various actions such as capturing flags and holding down territories also reward the player. Black Ops II remains popular today.

2 Call of Duty: Black Ops -- 26.2 million units sold

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The 1960s were a bevy of controversial military action in the U.S. Thus, it makes the perfect setting for a Call of Duty game. Black Ops absolutely blew up in sales, quickly breaking multiple sales records within days of its release. In terms of gameplay, the multiplayer aspect kept the kill streaks concept. This time around, the player had many more kill streaks to choose from. Customization is a huge player in Black Ops multiplayer, allowing the player to create their own emblems to place on their guns. A wide array of attachments and scopes were available to buy with "COD points" (points gained from winning matches and completing challenges. "Zombies" mode also made a return, arguably becoming the most popular aspect of Black Ops.

1 Call of Duty: Modern Warfare 3 -- 26.5 million units sold

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In terms of sales, everything came together for the concluding chapter in the Modern Warfare trilogy. Take the end of a series, new game modes, and an overhaul to kill streaks, and you get a recipe for massive sales. Infinity Ward tweaked their tried-and-true formula just enough to satisfy the general populace of gamers. As in previous titles, Modern Warfare 3 included a mode titled "Survival" (similar in nature to "Zombie" mode). Players have to work together to survive waves upon waves of enemies. Rewards abounded for players in the form of score streaks. With score streaks, players get rewarded for actions other than just killing their opponents. Though critics have given the game lower marks then most other titles, Modern Warfare 3 still sits at the top of the mountain in terms of sales. Can Advanced Warfare top this juggernaut? Only time will tell.